In the same way, monks, I have taught the Dhamma compared to a raft, for the purpose of crossing over, not for the purpose of holding onto. Understanding the Dhamma as taught compared to a raft, you should let go even of Dhammas, to say nothing of non-Dhammas."

What aspects of the Dhamma get grasped at?

What aspects of the Dhamma do/should we finally let go of at the end?

The dogmatists have claimed to have found the truth, others say that it cannot be apprehended; the Sceptics continue the search. Sextus Empiricus

The word "Dhamma" in this phrase can also be translated as little d "dhamma", signifying phenomenon. However, the way it is worded in this translation (whose translation is it?) has been rendered in such a way that it precludes the (little d) "dhamma" interpretation.

I believe this is referring to non-becoming, particularly applied during meditation practice. We should let go of fine-states of becoming, to say nothing of the coarser states.